Although water and ion transport by epithelia has been extensively studied during the last 25 years, several key pieces of information have yet to be obtained or are still in question. This includes accurate values for the passive (or possibly active) rate of water transport through epithelia, accurate values for the rate of passive and active ion transport through epithelia, and the precise manner in which epithelia regulate their size and the composition of their intracellular solution. The purpose of the present study is therefore to analyze the osmotic behavior of isolated epithelial cells.